Calculate Physical Properties of Coil


The coil is the most recognizable form of an inductor. Both inductors and electromagnets consist of wires wound around a bobbin or core form and the coiled wire is known as the winding. The center of the coil is referred as the core.

Each individual loop of wire is called a turn. To prevent short-circuit because of the turns the wire needs insulation, such as plastic or enamel coating. Finally to secure the winding, it is often wrapped around a coil form made of materials like plastic. In designing and constructing the coil like this, it becomes necessary to estimate the cross sectional area, and resistance of the coil.

This online electrical calculator helps you calculate the physical characteristics of a coil or material, including resistance, total wire length, and number of windings. The calculator assumes the wire to be copper when calculating resistance and voltage.

Wire Diameter
Number Of Turns
Bobbin Length
Bobbin Diameter


\[T= \frac {bl}{d}\]
\[n= \frac {Turns}{T}\]
\[cd = (2 * n * d) + bd \]
\[r= \frac {n * d + bd}{2}\]
\[a = \pi * r * r\]
\[L= \frac {2 * \pi * r * n}{1000}\]
\[rpm = 0.0333 * \frac {\left( \frac {0.812}{2}\right)^2}{\left(\frac{d}{2}\right)^2}\]
\[R= rpm * L\]
\[V = R * I\]
\[P= V* I\]

where :

  • T = Turns per winding,
  • bl = Length of Bobbin,
  • d = Wire Diameter,
  • n = Number of windings,
  • cd = Outer diameter of the coil,
  • bd = Diameter of Bobbin,
  • r = radius of the middle of the coil,
  • a = Cross-sectional area,
  • L = Total Length,
  • rpm = Resistance/meter,
  • R = Resistance,
  • V = Voltage at Rated Current,
  • I = Current,
  • P = Power at Rated Current,

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